Improving Precision and Accuracy in Coulombic Efficiency Measurements of Lithium Ion Batteries

Abstract

Lithium-ion batteries have been used extensively over the past two decades in the portable consumer electronics industry. More recently, Li-ion batteries have become candidates for much larger-scale applications such as electric vehicles and energy grid storage, which impose much more stringent requirements on batteries, especially in terms of cell lifetime. In order to develop batteries with improved lifetimes, a means of quickly and accurately evaluating battery life is required. The use of coulombic efficiency (CE) is an important tool in this regard, which provides a way to quantify parasitic reactions occurring within the cell. As more stable battery chemistries are developed, the rates of parasitic reactions occurring in the cell become reduced, and differences in CE among cells become increasingly smaller. In order to resolve these differences, charger systems must be developed which can measure CE with increased precision and accuracy. This thesis investigates various ways to improve the precision and accuracy of CE measurements. Using the high-precision charger (HPC) at Dalhousie University (built in 2009) as a starting point, a new prototype charger was built with several modifications to the design of the existing HPC. The effect of each of these modifications is investigated in detail to provide a blueprint for the development of next-generation charger systems. This prototype charger shows greatly improved precision and accuracy, with CE results that are approximately four times more precise than those of the existing HPC and over an order of magnitude more precise than high-end commercially available charger systems